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Add normabspath() to replace realpath(), making quark work with musl

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Compiled against musl, quark will not work as musl needs the presence
of procfs to process paths in realpath().
We could wait for it to be implemented[0] or also notice that we don't
want to overengineer the target-resolving. I don't think it's very
suckless if we deploy such a huge infrastructure to resolve paths.

To counteract this and given there are no good solutions available, I
set out to write the function normabspath(), which normalizes an
absolute path.
It is idempotent and works on the buffer passed to it. We don't need a
target, as the resulting resolved path is guaranteed to be of equal
length or shorter. This requires a memcpy in our case before calling it,
but I see it as a nice demonstration of the possibilities and it might
prove to be useful for other projects.

Not requiring a target buffer (that needs to have its length specified),
the one-string-call also simplifies the calling semantics drasticly.

With this function in place, quark works with musl. Statically linked,
stripped and with -Os, it only weighs 102K.

[0]: http://www.openwall.com/lists/musl/2016/11/03/5
This commit is contained in:
Laslo Hunhold 2017-06-21 10:27:17 +02:00
parent f4db83f68c
commit 283bf91a0e
1 changed files with 44 additions and 2 deletions
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46
quark.c
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@ -456,6 +456,47 @@ sendfile(int fd, char *name, struct request *r, struct stat *st, char *mime,
return s;
}
static int
normabspath(char *path)
{
size_t len;
int done = 0;
char *p, *q, *lastp;
/* force and skip first slash */
if (path[0] != '/') {
return 1;
}
p = path + 1;
/* get length of path */
len = strlen(p);
for (lastp = p; !done; ) {
/* bound path component within (p,q) */
if (!(q = strchr(p, '/'))) {
q = strchr(p, '\0');
done = 1;
}
if (p == q || (q - p == 1 && p[0] == '.')) {
/* "/" or "./" */
memcpy(p, q + 1, len - ((q + 1) - path) + 2);
len -= (q + 1) - p;
} else if (q - p == 2 && p[0] == '.' && p[1] == '.') {
/* "../" */
memcpy(lastp, q + 1, len - ((q + 1) - path) + 2);
len -= (q + 1) - lastp;
p = lastp;
} else {
lastp = p;
p = q + 1;
}
}
return 0;
}
static enum status
sendresponse(int fd, struct request *r)
{
@ -472,8 +513,9 @@ sendresponse(int fd, struct request *r)
}
/* normalize target */
if (!realpath(r->target, realtarget)) {
return sendstatus(fd, (errno == EACCES) ? S_FORBIDDEN : S_NOT_FOUND);
memcpy(realtarget, r->target, sizeof(realtarget));
if (normabspath(realtarget)) {
return sendstatus(fd, S_BAD_REQUEST);
}
/* reject hidden target */